1. Field of the Invention
The present invention relates to a temperature compensation circuit, for example, for using in a wireless communication device.
2. Background Art
In a wireless communication device, particularly, in a power amplifier (high-frequency power amplifier) for a transmission system, temperature compensation is required.
In general, when a temperature characteristic with respect to a gain of a common-emitter amplifier is desired to be flattened, a current that flows in the amplifier is set to a PTAT (Proportional To Absolute Temperature) current that has a temperature characteristic proportional to an absolute temperature. Theoretically, it is considered that the temperature characteristic of the gain is thereby to be flattened. For this reason, this method is frequently used as a temperature compensation method in the common-emitter amplifier.
However, for a high frequency signal, the temperature characteristic of the amplifier causes a decrease of the gain at a high temperature actually. The decrease of the gain is considered to result from various factors such as Ft (cutoff frequency) of a transistor and an increase in resistance of metal. For this reason, conventionally, the temperature compensation for the gain at a high temperature has been insufficient.
According to a technique disclosed in JP-A 2006-191482, the decrease of the gain at a high temperature is prevented by clamping a signal line by a diode to regulate a current that flows through the diode. However, this is not suited for a high-frequency processing circuit because a large loss is brought about in the diode. For this reason, even this conventional art cannot prevent the decrease of the gain at a high temperature.
Therefore, there is a demand for providing a temperature compensation circuit that can perform the temperature compensation of the gain at a high temperature. Particularly, because the decrease of the gain is attributed to various factors, there is a strong demand for providing a temperature compensation circuit that can finely adjust the temperature compensation.